The present invention relates generally to satellites, and more particularly, to systems and methods that raise the orbit of a satellite to geosynchronous orbit.
The assignee of the present invention manufactures and deploys spacecraft that orbit the earth. For satellites that are placed in geosynchronous orbit, the Van Allen radiation belts pose hazards for the satellite caused by radiation, and the like.
U.S. Pat. No. 5,595,360 entitled “Optimal Transfer Orbit Trajectory Using Electric Propulsion” addresses orbit raising maneuvers of satellites. Such prior art orbit raising techniques limit orbit maneuvers in terms of location and attitude to achieve and maintain the orbital semi-major axis near the geosynchronous value so that the satellite can be continuously observed from a single ground station. U.S. Pat. No. 5,716,029 entitled “Constant Sun Angle Transfer Orbit Sequence and Method Using Electric Propulsion” discloses a technique that adjusts the inertial attitude periodically while maintaining a fixed direction of electric propulsion thrust firing throughout each orbit. Prior art techniques also do not steer the thrust vector while also steering the satellite's attitude during the orbit to maintain the sun's illumination on the solar arrays of the satellite during orbit raising maneuvers. Steering the thrust vector maximizes efficiency of the delivered thrust thus minimizing fuel and time to achieve the desired final orbit.
Therefore, it would be advantageous to have improved systems and methods that raise the orbit of a satellite to geosynchronous orbit. It would also be advantageous to have improved systems and methods to minimize exposure of the satellite to the hazards of the Van Allen radiation belts.